My cat walks with his tail down. He also does not sit upright - instead he crouches very low or lies. Any thoughts?

My cat was diagnosed with a UTI 2 weeks ago. Before treatment he just howled, peed everywhere, and walked around very gingerly. He is now eating/drinking, using the litter box, and walking around. In addition, to the behavior above, the full energy level has not returned. He had some litter/waste stuck to his tail for a few days, but that is gone now and there has been little improvement over the past 48 hours.